The present invention relates to a process for producing phenol-dicarbonyl condensates of phenols with 1,2-dicarbonyl compounds which yields condensates that are very high in fluorescence and that can be glycidated with epihalohydrin and base to give epoxy resins which are also very high in fluorescence. The present invention further relates to the phenol-dicarbonyl condensates, epoxy resin systems and laminates made with the phenol-dicarbonyl condensates obtained and the phenol-dicarbonyl condensates of the present invention as curing agents in an epoxy resin system.
Condensates of 1,2-dicarbonyl compounds with phenol compounds, especially the condensate of glyoxal with phenol (tetraphenolethane, TPE), are important intermediates for making specialty epoxy resins. Epoxy resins made from these materials are extensively used, especially in the electrical laminating industry, for increasing the glass transition temperature (Tg) of epoxy resin systems through their multifunctionality and particularly for facilitating printed wiring board inspection through their fluorescence. It is commercially desirable that these epoxy resins be high in fluorescence for maximum efficiency of use for printed wiring board inspection.
Prior art techniques for preparing these phenolic precondensates include the condensation of the phenol with the 1,2-dicarbonyl compound using a strong acid such as sulfuric or methanesulfonic acid, followed by neutralization of the acid with an aqueous solution of a material such as sodium hydroxide or sodium bicarbonate, extraction of the resultant salt with water, and isolation of the phenolic condensate product by evaporation of phenol and water from the organic layer. Alternative techniques include the use of a volatile strong acid such as hydrochloric acid, or an acid which decomposes to volatile materials at temperatures above 100xc2x0 C. such as oxalic acid, as the catalyst. Use of these decomposable or volatile acids eliminates the need for neutralization or extraction before evaporation of the phenol. The above processes, however, tend to produce material of relatively low fluorescence.
It has now been found that when one or more carboxylic acid(s) or carboxylic acid precursor(s) are used as catalysts for the condensation reaction of phenolic compounds with 1,2-dicarbonyl compounds, phenol-dicarbonyl condensates with a high ratio of fluorescence to Gardner color are produced. These phenol-dicarbonyl condensates can be used to produce epoxy resins, epoxy resin systems, and laminates which are also high in fluorescence.
The present invention provides a process for producing phenol-dicarbonyl condensates high in fluorescence by reacting a phenolic compound with a 1,2-dicarbonyl compound in the presence of a catalyst selected from one or more carboxylic acid(s) or one or more carboxylic acid precursor(s). The present invention further provides phenol-dicarbonyl condensates, epoxy resins, epoxy resin systems and laminates prepared using these phenol-dicarbonyl condensates.